Multi-storage node pixels may be beneficial in high dynamic range (HDR) imaging, which may include overlapped-exposure imaging techniques. In overlapped-exposure HDR imaging, multiple images are captured with an image sensor over the same time period but with different exposure periods, and the images are later combined into a high dynamic range image.
Images captured at different times for the purpose of HDR imaging may result in distorted images for moving objects. Capturing images in an overlapped manner reduces the distortion as multiple image captures receive the same motion at the same time.
Rolling shutter architectures also result in image distortion for moving objects since images are captured in a sequential row-by-row fashion. As such, a global shutter design may be preferred to minimize the motion distortion associated with rolling shutter circuits, since all pixels in a global shutter imager integrate light simultaneously.
Conventional global shutter pixels capable of correlated doubled sampling have at least one photo sensitive element, a dedicated in-pixel storage region, and a floating diffusion region. The pixels operate by transferring charge to the storage region after integration, resetting the floating diffusion region prior to readout, and then reading out the charge from the storage region to the floating diffusion region for sampling. As such, the floating diffusion region is utilized only during the readout period.
Creating a HDR image utilizing a global shutter design with pixels formed with multiple storage regions results in larger pixels, or for a given pixel size, reduces the area for the photodiode, thus decreasing sensitivity.